Stable emulsions of vinyl esters



Patented Apr. 16, 1946 s'rms smsross or vnvn. ss'rsas Hem-y Michael Collins and Mogens Kiar, Showinlgan Falls, Quebec, Canada, aslignors to Shaw- Inigan Chemicals Limited,

West Montreal.

Quebec, Canada, a corporation of Canada No Drawing. Application November 11, 1942, Se-

I'lal No. 465,280.

In Canada October 21, 1942 6 Claims. (Cl. 280-32) INTRODUCTION This invention relates to polymerization of vinyl esters in emulsion.

There are relatively few emulsifiers which are operative to maintain the stability 01' such an emulsion over the relatively wide range of temperatures incidental to the polymerization process. One sug estion is made in U. 8. Patent No. 2,227,163, which discloses the polymerization of polyvinyl acetate in aqueous emulsion using as an emulsifier polyvinyl alcohol or its water-soluble derivatives. The alcohol itself is the only such body exemplified.

The applicant has round that polyvinyl alcohol and certain of its water-soluble derivatives are in many respects inefl'ective in producing stable aqueous emulsions of polyvinyl esters. In some cases, while'emulsions can be formed, they are either unstable or inherently unstable. In other cases, stability is achieved only when a consicb erable amount of monomeric vinyl ester remains in the emulsion.

Osncrs Having regard to these circumstances, it is an object of the present invention to provide stable aqueous emulsions of polyvinyl esters low in residual monomer; a process or emulsifying by the use as emulsifiers of certain partially hydrolyzed polyvinyl acetates eilective to term stable emulsions low in residual vinyl ester; 8 process in which foaming during the mixing of the constituents is reduced to a minimum.

These objects are accomplished by employing as emulsifiers, in the emulsion polymerization of vinyl esters, partially hydrolyzed polyvinyl acetates having an acetate group content of between about 10 percent and about 43 percent. These materials are eilective at concentrations between about 1 and about 6% by weight or the total charge to form an emulsion having a polyvinyl acetate content ranging from about 30% to about 70% by weight and to protect the emulsion during polymerization and afterwards under the normal conditions of handling and storage. Conversion of the monomer to a polymer having a viscosity within the useful range. 1. e.. from about 1.5 to about 300 centlpoises. can be carried to substantial completion by conducting the polymerization for about 50 to about 300 minutes under reflux at a temperature from about 66 C. to about 90 (2., in the presence or a peroxide catalyst at a concentration within the range efl'ective to provide available oxygen from about 909% to about .4'1% by weight of the vinyl acetate so as to reduce the amount oi monomer remaining in the emulsion to from about 2% to about .3% by weight 01' the emulsion without destroying the stability 0! the emulsion.

Exnnus In order that the invention may be understood in more detail, various embodiments are illustrated in the following examples. These examples are intended as explanatory only and not limiting to the scope of the invention.

For polymerizing in emulsion according to the procedures to be described, an apparatus is employed having characteristics and dimensions approximately as follows. The container is an al minum pot 8 inches high by 6 inches diameter having a concave bottom and no bames. The stirrer is of stainless steel. It embodies hall an inch from the bottom, 4 blades in a cluster 1 inch by hali' an inch bent at an angle of 45 degrees tor downward thrust; four inches from the bottom a pair of blades 2 /2 inches by three quarters of an inch bent at an angle or 45 degrees for downward thrust. The useful speeds of the blades are about 500 to about 1500 revolutions per minute. The pot is equipped with a reflux condenser.

The following Examples 1 to 9 as given in Table 1, illustrate the-use of various partially bydrolyzed polyvinyl acetates in the emulsion polymerization or vinyl esters. In these runs, the

charge employed and the characteristics 01' the reaction are substantially as follows:

Approximate concentration Comma and other factors Emulsiiler partially hydrolyzed polyvinyl acetate havin the ace.- tate group content in icated in Table l, and made irom polyvinyl meg-gate of viscosity about 7 centle Surface tension-"Aerosol O. T."

depressant.

Medium-water Monomawvinyl acetate...

2.5%, by weight of the total c arge.

(it? by weight oi the total 537 gains. 090 grams. .W grams Catalystbeusoyl pcroxidm (.17 on v. a.). Stirring speed 1,200 a. P. M?

Time of polymerlzatiom, 2 hours.

Temperature at reflux Min. 66 0., max. 84 C.

benzoyl peroxide catalyst is then added and the whole charge brought to reflux temperature of about 66 C. The run is completed when the temperature has reached the neighborhood assasss The results of the respective tests all indicate that the emulsions made with agents having an acetate group content or about or over are Those made with partially hydrolyzed stable.

80 C. to 85' C. The charge is then cooled and 6 polyvinyl acetates containing less than about 10% removed from the kettle. acetate groups were indicated as unstable. Other The approximate results or using the diflerent characteristics of all the stable emulsions were patrzidallaylhydrolyelliflpojlyflgygeacetgsifilstsare indisubstantially as follows, after cooling.

on cow in a e se r are exon pressed in terms of stability as determined by 10 Propel-t1 of Bonds fi 8 Egg? 0! certain tests developed by the applicant e8 Residual vinyl acetate 2 percent by weight of n the total charge (a) The gravity settling test consists oi let- Emulsion viscosity 200 centipolses ting the emulsion stand for a time and t n pH 5.0 measuring the amount 01' precipitation i. e. sludg- Palmer viscmlty 125 cenflpoms mg, 11 there ha been substantially no precipi Particle size or the poly- Between about 0.5 and tion in seventy-two hours, the emulsion is convinyl acetate. about 44), sidered stable. Em m l 10 (b) The hot stir test consists of heating the a emulsion from room temperature t bout 0 c, This example demonstrates that stable emulwith slow stirring at about 600 R. P. M. and then 510118 08-11 e ma e with a partially y roly ed stirring the emulsion at about 1200 R. P. M. for P lyvinyl acetate having an cetate group omit-ant about 5 minutes. If any substantial coagulation oi less than 10%. provi a relatively hi h o is observed after this time, the emulsion is coneentration of m n m ri vinyl a etate remains sidered unstable. imerom- (c) viscoslty increase t t" consists of The nature of the constituents of the charge, drawing a sample from the charge after polymerapproximate concentrations and results of submuon, at about Q allowing t sample 1; iecting the charge to polymerization conditions 0001 to about Q without u and then substantially as in Examples 1-9 are as follows: measuring its viscosity. The bulk or the emul- 30 Per cent sion is then cooled to about 20 C. with stirring Partially hydrolyzed polyvinyl acetate havand its viscosity measured and compared with ing an acetate group content of about that oi the first sample. It the viscosity of the m fr m p lyvin l acetate havsainple cooled without stirring shows a marked ing a viscosity of about 7 centipoises 1 2.5 increase (about 15 centipoises or more) M7551 that "Aerosol 0. 1 oi the emulsion cooled with stirring, insta ty is indicated. This is substantiated by microscopic Taken by weight on the total charge. Grams examination which shows t at the i e in w t 0o emulsion viscosity is to the mlescence the Vinyl seems--- I III IIIIIIZZIII" 90o Particles 01 ha i y peroxide o 9 (d) The centrifuge test consists in centrltuging the emulsion at about 1950 R. P. M. for about Condition of reaction 20 inut (about 20 c Stirring sp d 1200 R. P. M.

The sludge resulting is recorded as a percentage 5 Time 01 polymerization 1 hr., 10 mins. of he total emulsion. Where the sludge content Temperature at reflux is substantially nil, the emulsion is considered min. 66 C. good. Where there is a slud e content oi about Resulting emulsion (after cooling) 10% or below, the emulsion is considered fair. vismsity of the polymer 51 centipolses Above 10%, the instability increases with the per- 50 Emulsion-viscosity centipoises. centage. Residual vinyl acetate 10 per cent by weight (e) Veriiication." The results of the above on the total charge tests are verified by checking one against the Percent solids 40 per cent by weght other. on the total cl large Table 1 "Viscosity increase m" c t K Hydro "Gravity settling u t es t use lm Hot stir test P V- A mt m Miscroscopic data 2.517 80% ppted. in 72 hrs--. Unstable 50 3.6:? 21% pptcd. in 72 hrs... -do 75 5.8:7... 70% pptod. in 721111... .do um 20% ppted. in 7211... do 40 8.5:7 5% ppted. in 72 m.-. Moderately stable. 40 10:7 Btab1eto72hrs Stable 10 18:7 ...--do 8 2051--..-- --...do..... do.-... 0 31:1 do (In o The charge was tested for stability substantially as in the preceding Examples 1 to 9 with the following approximate results.

Hot stir test Stable Centrifuge test sludge Viscosity increase test 3 centipoises increase Emnsrrvmc Acnnrs In accordance with the invention, the partially hydrolyzed polyvinyl acetates which are useful as emulsifiers in producing stable emulsions are those having an acetate group content of between about and about 43%, i. (-2., calculated on a weight basis as vinyl acetate. Those having an acetate group content of between about 10% and about 25% have the additional characteristic of forming an emulsion which does not foam during stirring. This is a distinct advantage, since, if the monomer in the emulsion tends to foam, the difliculties of controlling polymerization are such that the final emulsion is generally unstable. The tendency to foam is particularly pronounced where certain hydrophilic colloids are used in conjunction with the partially hydrolyzed polyvinyl acetate, for instance, as described in Collins co-pending application Serial No. 457,338, filed on Sept. 4, 1942, now U. S. Patent 2,388,601. The remainder of the range, namely, the partially hydrolyzed products having an acetate group content of between about 25% and about 43% are especially good emulsifiers, but do not possess the non-foaming advantage.

Vrscosn'rv-Concsnranrrow The partially hydrolyzed products may be made from polyvinyl acetates having various viscosities within the range of about 1.5 to about 200 centipoises. The concentration will, however, vary with the viscosity of the polyvinyl acetate from which it is made. For instance, where the viscosity of the starting polyvinyl acetate is about 7 centlpoises the preferred concentration for a partially hydrolyzed polyvinyl acetate having an acetate group content of about 31% is in the neighborhood of 2.5% calculated by weight on the total charge.

The preferred concentrations of agents made from polyvinyl acetates of other viscosities are those effective to form solutions in a given quantity of water of viscosity equivalent to a, near 10% solution of an agent made from a polyvinyl acetate having a viscosity of about 7 centipoises. The operative concentration may vary between amounts effective to give solutions equivalent to those of between about 4.0% a d about 15.0% of the '7-viscosity agent. The agent in all cases must, of course, have been hydrolyzed to the approprlate degree. The preferred agents are made from polyvinyl acetates of viscosity between about 7 centipoises and about 60 centipoises. The onerative range of concentration will vary as noted above depending on the viscosity, between about 1.0% and about 6.0% calculated by weight on the total charge.

Srssruzmc Errnc'r These emulsifiers are unique in being capable of stabilizing the emulsion-emulsoid over the relatively wide range of temperatures encountered. They are capable (a) of acting as a liquid/liquid phase emulsifier at the commencement of the process, at say about 20 C. (b) of protecting the emulsion at about 66 C. (the start of reflux) and finally, (c) of protecting the solid/liquid phase both at the maximum temperature encountered in polymerization at about 83 C. and afterwards at room temperature or lower, sometimes down to about 0. The partially hydrolyzed polyvinyl acetates specified may also be used in combination with other emulsifying agents as for instance, disclosed in copendlng application, Serial No. 457,- 338, filed Sept. 4, 1942, H. M. Collins. now U. 8. Patent 2,388,601.

Seance Tension Dsrazsssursrmamc The use of depressed surface tension also help to obtain a stable emulsion and to eliminate the necessity for complex stirring, and is thus preferred. This condition may conveniently be accomplished by using a suitable depressant. "Aerosol O. T. (the sodium salt of the sulphonic acid of dioctyl succinic ester) is satisfactory. Other surface tension depressants may be used, as for instance, the other Aerosols, Aresklene," fatty acid soaps of hydroxyethyl ethylene diamine, fatty acid soaps of Merpentine, sulphonates of high alcohols and alkyl aryl type wetting agents. A criterion of utility in that the depressant has to be compatible and non-reactive with the other constituents of the charge. The concentration of surface tension depressant should be in the range of between about 0.05% and about 3.0%.

The type of stirring is not complicated as will be clear to one skilled in the art. It will vary somewhat with different types of equipment. In the particular equipment described above, which was used to carry out the procedures of the examples, the stirring should be of the order of between about 700 and about 1500 R. P. M. Where this speed is greater or less than this range, the emulsion tends to be unstable. At the low speeds great care should be taken to control reflux, rate of charging etc., to lessen foaming and other undesirable results. Partially hydrolyzed polyvinyl acetates having an acetate group content of between about 10% and about 25% acetate groups are characterized by causing considerably less foaming than other of the partially hydrolyzed bodies.

Pieferred conditions for the particular anparatus described can be achieved by charging the vinyl acetate at a low rate, at say, about 500 grams per minute, operating the stirrer at a rate of about 1200 R. P. M. in the equipment aforementioned and operating at a low reflux rate, at about 1.0% of the total charge per hour.

The CATALYST Any organic or inorganic peroxide may be used as a catalyst in carrying out the reaction. Benzoyl peroxide or hydrogen peroxide are preferred. Hydrogen peroxide is employed preferably at a concentration of between about .02% and about 1.0% (available oxygen between about 009% and about .4'7%) calculated by weight on the monomer, supplemented by an amount of an alkaline accelerator such as, for instance, sodium bicarbonate, effective to bring the pH of the charge at the start of the reaction to between about 6.5 and about 9. Regulation of the proportions of catalyst to control the reaction and to give predetermined characteristics to the resulting polymer is taught by Kiar in copending application Serial No. 457,339, filed on Sept. 4, 1942. Where high concentrations of catalyst are employed, it may also be necessary to use small quantities of a controlling agent such as acetaldehyde to control the reaction and the characteristics of .the resulting polymer as also taught by Kiar in the copending application referred to. The polymerization time will vary between about 50 minutes and about 800 minutes. The rate of addition of the vinyl ester may vary between about 2 and about minutes. The ratio oi vinyl acetate to water should be between about 30% and about. 70% by weight.

POI-WHO! PROCEDURE In a characteristic procedure, the emulsifying agent is added to the water and the charge stirred for about 5 minutes. The catalyst is added with stirring, the vinyl acetate is added to the aqueous phase with stirring. The charge is then stirred for about 5 minutes after which it is brought to reflux temperature with stirring and gentle reflux kept up by the temperature manipulation until reflux temperature has gone from about 66 C. at commencement to about 84 C. at the finish. The charge is then cooled slowly with stirring to about 25 C. and drained.

Conversion of the monomer may be carried to substantial completion without destroying the stability of the emulsion. This is not possible with polyvinyl alcohol as the emulsifier. Generally the residual vinyl acetate remaining in an emulsion made according to the present invention is between about 0.3% and about 5.0% by weight or the emulsion so that the emulsion may be said to be substantially free from monomeric vinyl ester.

Tm: Emunsom The emulsoid formed is stable up to the high temperatures reached in polymerization that is up to about 90 C. and down to the low temperatures that is about 0 C. which might be encountered in storage and transit when the usual precautions are taken. This stability may, for practical purposes, be considered as permanent, since it persists for the period demanded by the market. Generally, emulsions 01' this type are used within about six months or sooner.

The characteristics of the emulsions may be modified to some extent according to the particular conditions employed in its manufacture. The viscosity of the finished emulsoid may vary between about '100 centipoises and about 300 centipoises. The viscosity of the polyvinyl acetate may be varied between about 1.5 centipoises and about 300 centipoises, as for instance, disclosed in Kiar copending application Ser. No. 457,339. The high solid content of these emulsoids as compared with solutions is advantageous especially for him forming. Films may be laid down which are unexpectedly pliable and nonblocking. The polymer may also be recovered from the emulsion by precipitation with electrolytes, as for example, aluminum sulphate with ammonia, or boric acid.

The emulsoid may be modified by adding at any convenient time, solvents, plasticizers, fillers, pigments, etc., or the types usually employed with the particular polymer forming the dispersed phase and which are inert to the constituents of the charge. For instance, in the case 01' P LY- vinyl esters, suitable plasticizers are dibutylphthalate and "3 G. H." Suitable fillers are iron oxide and titanium oxide. Since these agents can usually be added after polymerization has been completed there is not thought to be any great advantage in adding them during the process.

Uses

There are many uses to which these resins may be applied in emulsoid or solid form, for instance:

As grease proof coatings for articles mad oi sheet fabrics such as cloth. paper and cardboard. They may be pigmented, filled and/or plasticized.

For impregnating porous materials.

As adhesives and heat sealing compositions.

For compounding with other materials. fillers, for example, to give tough, resilient end products.

its vehicles ior carrying metal powders, dyes, caflblon black and other electrically conductive so s.

As a chewing gum base.

As a. vehicle to bind pigments in coatings.

POLYMERS FORMED While the invention has been described principally in connection with the polymerization of vinyl acetate since preferred results are achieved with this body, it may also be applied to the polymerization of other vinyl esters such as vinyl propionate, vinyl butyrate and vinyl chloride. Copolymerization of two or more vinyl esters may be accomplished.

Water has been named as the non-solvent vehicle for the emulsion. It will be understood that the monomeric substances can be polymerized in any non-solvent vehicle in which the emulsifying agents are operable, but water is most economical and is highly satisfactory.

The term stable" is used to denote the capacity of the emulsion-emulsoid to retain its form as such for the period demanded by the market under the conditions encountered during polymerization and during commercial handling, in contrast to the tendency of many emulsion-emulsoids to "break under these conditions.

It will be understood that. without departing from the spirit oi the invention or the scope of the claims, various modifications may be made in the specific expedients described. The latter are illustrative only and not offered in a restricting sense, it being desired that only such limitations shall be placed thereon as may be required by the state of the prior art.

The sub-titles used throughout the specification are merely to simplify reference thereto and should otherwise be disregarded.

We claim:

1. A process of preparing a stable aqueous emulsion of polyvinyl acetate having a viscosity within the range from about 1.5 to about 300 centipoises, comprising, emulsifying in water vinyl acetate in the presence of a partially hydrolyzed polyvinyl acetate containing between about 10% and about 43% acetate groups at a concentration from about 1% to about 6% by weight on the total charge, the ratio of vinyl acetate to water being between about 30% and about 70% by weight, and heating and stirring said emulsion in the presence of a peroxide catalyst at a concentration selected from the range to provide available a concentration selected from the range to provide available oxygen from about .009% to about .47% by weight of the vinyl acetate for about 50 to 300 minutes under reflux at a temperature from about 66 C. to about 90 C. thereby to convert the monomer to a point where only from about three tenths to about two percent of monomer based on the weight of the emulsion remains and a stable emulsion is formed.

2. A process of preparing a stable aqueous emulsion containing a polyvinyl acetate, according to claim 1, wherein the partially hydrolyzed polyvinyl acetate has an acetate group content between about 10% and about 25 aaoas 3. A process of preparing a stable aqueous emulsion containing a polyvinyl acetate, accordingtociaimLwhereintheportiallyhydrolyiwd polyvinyl acetate has an acetate group content between about 25% and about 43% 4. A process of preparing a stable aqueous emulsion containing polyvinyl acetate accordn: to claim 1 wherein the partially hydrolyzed polyvinyl acetate has an acetate group content oiabout 18%.

5. A process of preparing a. stable aqueous about 31%.

HENRY MICHAEL COLLINS. MOGENS KIAR.

Certificate of Correction Patent No. 2,398,344.

April 16, 1946.

HENRY MICHAEL COLLINS ET AL.

It is hereby certified that the residence of the assi use in the above numbered patent was erroneously described whereas said residence should have been d and specified as West escribed and specified as Zl lontreal, Quebec,

ontreal, Quebec, Canada,

Canada; as shown by the records of assignments in this ofiice; page 4, second column,

lines 61 and 62, claim 1,

strike out the Words a to proyide available; and that the said Letters corrections therein that the same may conform to concentration selected from the range Patent should be read with these the record of the case in the Patent Signed and sealed this 6th day of August, A. D. 1946.

LESLIE FRAZER,

First Assistant Gammissioner of Patents.

aaoas 3. A process of preparing a stable aqueous emulsion containing a polyvinyl acetate, accordingtociaimLwhereintheportiallyhydrolyiwd polyvinyl acetate has an acetate group content between about 25% and about 43% 4. A process of preparing a stable aqueous emulsion containing polyvinyl acetate accordn: to claim 1 wherein the partially hydrolyzed polyvinyl acetate has an acetate group content oiabout 18%.

5. A process of preparing a. stable aqueous about 31%.

HENRY MICHAEL COLLINS. MOGENS KIAR.

Certificate of Correction Patent No. 2,398,344.

April 16, 1946.

HENRY MICHAEL COLLINS ET AL.

It is hereby certified that the residence of the assi use in the above numbered patent was erroneously described whereas said residence should have been d and specified as West escribed and specified as Zl lontreal, Quebec,

ontreal, Quebec, Canada,

Canada; as shown by the records of assignments in this ofiice; page 4, second column,

lines 61 and 62, claim 1,

strike out the Words a to proyide available; and that the said Letters corrections therein that the same may conform to concentration selected from the range Patent should be read with these the record of the case in the Patent Signed and sealed this 6th day of August, A. D. 1946.

LESLIE FRAZER,

First Assistant Gammissioner of Patents. 

